Conventional turbomolecular vacuum pumps include a housing having an inlet port, an interior chamber containing a plurality of axial pumping stages and an exhaust port. The exhaust port is typically attached to a roughing vacuum pump. Each axial pumping stage includes a stator having inclined blades and a rotor having inclined blades. The rotor and stator blades are inclined in opposite directions. The rotor blades are rotated at high speed to provide pumping of gases between the inlet port and the exhaust port. A typical turbomolecular vacuum pump includes nine to twelve axial pumping stages.
Variations of the conventional turbomolecular vacuum pump are known in the prior art. In one prior art vacuum pump, a cylinder having helical grooves, which operates as a molecular drag stage, is added near the exhaust port. In another prior art configuration, one or more of the axial pumping stages are replaced with disks that rotate at high speed and function as molecular drag stages. A disk which has radial ribs at its outer periphery and which functions as a regenerative centrifugal impeller is disclosed in the prior art. Turbomolecular vacuum pumps utilizing molecular drag disks and regenerative impellets are disclosed in German Patent No. 3,919,529, published Jan. 18, 1990.
While prior art turbomolecular vacuum pumps have generally satisfactory performance under a variety of conditions, it is desirable to provide turbomolecular vacuum pumps having improved performance. In particular, it is desirable to increase the compression ratio so that such pumps can discharge to atmospheric pressure or to a pressure near atmospheric pressure. In addition, it is desirable to provide turbomolecular vacuum pumps having increased pumping speed and decreased operating power in comparison with prior art pumps.
It is a general object of the present invention to provide improved turbomolecular vacuum pumps.
It is another object of the present invention to provide turbomolecular vacuum pumps capable of discharging to relatively high pressure levels.
It is another object of the present invention to provide turbomolecular vacuum pumps having relatively high pumping speeds.
It is a further object of the present invention to provide turbomolecular vacuum pumps having relatively low operating power.
It is a further object of the present invention to provide turbomolecular vacuum pumps having high compression ratios for light gases.
It is still another object of the present invention to provide turbomolecular vacuum pumps which are easy to manufacture and which are relatively low in cost.